The present invention relates generally to constant lighting systems and more specifically to a system and method for providing backlight for a liquid crystal display.
In the manufacture and use of liquid crystal displays, backlighting from a light source is dispersed evenly beneath the surface of a liquid crystal display to allow optimal viewing of the display in all types of ambient light conditions. Depending upon the light conditions of the environment, the light intensity of the backlight may be adjusted to allow optimal viewing of the liquid crystal display. Liquid crystal display backlights frequently employ fluorescent lamps. However, fluorescent lamps require high power and a high voltage source. Another method of providing backlight is through the utilization of light emitting diodes. Light emitting diodes are utilized for backlights in liquid crystal displays due to their dimming range, low-temperature performance, and efficient heatsinking attributes.
A collection of light emitting diodes may be connected serially or in parallel to form a backlight for a liquid crystal display. It is known to the art to flash light emitting diodes of a backlight on and off in a rapid fashion such that it appears to provide a constant light source. Flashing of the light emitting diodes has been accomplished by the switching of the current producing source, either a voltage source or a current source. However, switching of the current producing source can not be accomplished quickly, thus affecting the ability to adjust the light intensity level of the backlight. Slow switching of the current producing source does not allow a wide range of dimming of the backlight. Further, switching of the current producing source increases electromagnetic interference and noise within the backlighting circuit. Consequently, it would be advantageous if a system and method existed which allowed a wide dimming range and allowed for rapid flashing of light emitting diodes. It would also be advantageous if a system and method existed for flashing of light emitting diodes which could reduce the amount of electromagnetic interference and noise within the circuit.
Accordingly, the present invention is directed to a system and method of directing the flow of current supplied for a collection of light emitting diodes on an alternating cycle which allows for rapid flashing of light emitting diodes and provides a wide dimming range. A fixed amount of current may be available to the collection of light emitting diodes where the flow of the current may be controlled by an alternating periodic signal such that current passes through the light emitting diodes for predefined and discrete periods. During periods of time that current is not flowing through light emitting diodes, the current may be directed to flow in another area of the circuit. The duty cycle of the alternating periodic signal may be adjusted in order to vary the dimming capability of the LED backlights. Since the light emitting diodes may be controlled by directing the flow of current rather than by switching of the current producing source, less electromagnetic interference and noise may be present within the system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.